Scoliosis is an orthopedic condition characterized by abnormal curvature of the spine, with varying degrees of lateral curvature, lordosis and rotation. Despite extensive research, the pathogenesis of scoliosis remains obscure in the majority of cases.
The vertebral column is composed of vertebra, discs, ligaments and muscles. Its function is to provide both mobility and stability of the torso. Mobility includes rotation, lateral bending, extension and flexion. Scoliotic curvature is associated with pathologic changes in the vertebra and related structures. Vertebral bodies become wedge-shaped, pedicles and laminas become shorter and thinner on the concave aspect of the curve. Apart from the obvious physical deformity, cardiopulmonary problems may also present. As curvature increases, rotation also progresses causing narrowing of the chest cavity. In severe deformities, premature death is usually caused by respiratory disease and superimposed pneumonia.
Treatment options have varied little over the past few decades, and only two treatments effectively help correct scoliosis: spinal bracing with exercises and surgery. A properly constructed Milwaukee or low-profile brace will aid some patients with minor scoliosis. However, if the scoliosis progresses despite such bracing, or if there is substantial discomfort, surgical correction involving fusion of vertebra may be required. Surgery has traditionally involved procedures such as the Harrington, Dwyer and Zielke, and Luque procedures which rely on implanted rods, laminar/pedicle hooks, and screws to maintain the correction until stabilized by fusion of vertebrae.
Thus the goal of current surgery is to strip the paraspinal muscles from the lamina of vertebra to be fused, and effect correction and spinal fusion in one step. The general technique is as follows:                1. The outer cortex of the lamina and spinous processes is removed so that raw cancellous bone is exposed.        2. Posterior facet joints are destroyed and usually autogenous bone graft added. Graft is usually placed along the entire fusion area. The fusion extends from one vertebra above the superior end-vertebra involved in the curvature to two below the inferior end-vertebra of the curve.        3. Spinal instrumentation is applied. A distraction rod allows the spine to be ‘jacked’ up on the concave side of the curve. A compression assembly may be used on the convex side of the curve to ‘pull’ the curve straight. Anchors, laminar hooks, and/or wires are placed around the lamina to provide fixation for the rods.        
Yet other surgical procedures involve memory metal implants (Sanders, A Memory Metal Based Scoliosis Correction System, CIP-Data Koninklijke Bibliotheek, Den Haag, 1993), fusion of vertebra anteriorly, using anterior cages (e.g., Harms cage, from DePuy-AcroMed Inc.). Nevertheless, it is clear that available procedures have drawbacks including the requirement for substantial prosthetic implants (see Mohaideen et al., Pediatr. Radiol. 30:110-118 (2000) for a review) and complicated surgical procedures, often only partly correct scoliotic deformities, and result in reduced flexibility of the spine.